In communication systems, for example, digital wireless or the like, received data symbols are corrupted by distortion caused by impairments in the communication channel over which they were transmitted and by noise. Additionally, the data symbols are also corrupted by carrier frequency offset caused by disparity in the frequencies of a remote transmitter and a local receiver.
In orthogonal frequency division multiplexing (OFDM) systems, carrier recovery is necessary to compensate the carrier frequency offset at the receiver. As shown in FIG. 1, the carrier recovery typically includes use of a frequency offset estimator 101, a loop filter 102 and a rotator 103. The frequency offset estimator 101 is crucial in the performance of OFDM systems. Most frequency offset estimators 101 employ a certain correlation of the cyclic prefix of OFDM frames, i.e., symbols, in the time domain. While these prior approaches have been widely used, the performance of such frequency offset estimators is sensitive to such factors as length of the cyclic prefix, signal to noise ratio (SNR) and intersymbol interference (ISI). In the presence of intersymbol interference (ISI) the cyclic prefix samples may have large errors because of prior transmitted OFDM samples. Such errors introduce inaccuracy into the estimate of frequency offset in those systems employing the cyclic prefix in the computation. Additionally, these prior approaches to frequency offset estimation are especially disadvantageous in packet transmission systems, one example being a wireless local area network (WLAN), because in such systems, it is important to have an accurate estimate of carrier frequency offset so that the synchronization can be quickly established.